This invention relates to a system for adding an additive to the fuel of an internal combustion engine. More particularly, this invention relates to a new and improved catalyst metering system for adding measured quantities of catalyst to the fuel tank of the engine for purposes of emission control.
In order to comply with governmental and environmental exhaust emission standards for diesel engines, the removal of particulate matter from diesel exhausts has become a key method for emission control. The passing of the engine exhaust through emission control traps which typically have a relatively large surface area formed by a ceramic material has been found to be an efficient and effective means for removing particulate matter from the engine exhausts. The particulate matter from the engine exhaust collects in the trap and gradually forms layers of soot. During the operational life of the engine, the soot layers continue to amass in the emission trap. If unchecked, the collected soot eventually reaches a stage wherein the exhaust passage through the trap is obstructed. Even partial obstruction of the passage can result in back pressures which detract from the engine performance. While replacement of the trap or reconditioning of the trap such as by external ignition of the soot are options, the most efficient and advantageous use of the emission trap system resides in continuously regenerating the trap while the engine is operating. An effective means for regenerating the trap is to effect combustion of the soot collected in the trap. It has been established that the addition to the diesel fuel of a catalyst such as manganese or cerium additives forming a carboxylic acid is an effective means for lowering the self-ignition temperature of the soot layer to provide trap regeneration without a requirement of external ignition. Self-regeneration of a ceramic trap at exhaust gas temperatures of less than 250.degree. C. can be obtained.
The effectiveness of the catalyst additive/emission trap system for removing particulate matter from the exhaust of the diesel engine has resulted in a number of proposals for systems for adding the catalyst to the fuel. The quantity of catalyst required is very slight, i.e., on the order of five to six gallons for the normal 100,000 mile engine life expectation. However, because the catalyst tends to separate from diesel fuel if the fuel catalyst mixture remains unagitated for prolonged periods of time, in practice the catalyst is effective only if the catalyst is added to the fuel relatively shortly before the fuel is used. Precise metering of the catalyst is ordinarily not required.
One catalyst additive system employs a five gallon additive tank which is placed in the trunk of the vehicle and a pump is employed to pump the catalyst to the fuel tank. The fuel tank is modified to include a T-shaped mixing conduit, a check valve, and distribution pipes. The additive pump is external of the fuel tank. The pump is actuated in response to a fuel alert switch in the fuel fill pipe and a voltage which is supplied from the fuel level gauge in the fuel tank. A second additive metering system forces the catalyst additive through a metering valve into a line leading to the fuel injection pump. The action of the fuel injection pump functions to mix the fuel and the fuel additive. The fuel additive mixture which is not directly consumed by the engine is returned to the fuel tank and cooled in the tank with the aid of a heat exchanger.
The present invention is a new and improved additive metering system which provides for the addition of an additive to the fuel in the fuel tank in an efficient and reliable manner without requiring extensive modification to the fuel supply systems of the engine.